function selectstart()
{
  window.event.cancelBubble = true;
  window.event.returnValue = false;
  return false;
}
function checkall(form)
{
for (var i=0;i<form.elements.length;i++)
  {
  var e = form.elements[i];
  if (e.name != 'chkall')
     e.checked = form.chkall.checked;
  }
}
function lockalt()
{
   if(window.event.altKey)
     {
       alert("请选择退出系统！否则您下次将无法登陆！");
     }
}